Induced draft boiler fan structure



June 2, 1959 F. "A. LOEBEL INDUCED DRAFT BOILER FAN STRUCTURE Filed Jan.20, 1956 fieciewjck United States Patent INDUCED DRAFT BOILER FANSTRUCTURE Frederick A. Loebel, Milwaukee, Wis, assignor toCleaver-Brooks Company, a corporation of Wiscousin Application January20, 1956, Serial No. 560,308

3 Claims. (Cl. 122149) This invention relates to boilers and moreparticularly to the fan structures of induced draft boilers for inducinga draft in tubes forming multiple passes through the boiler forcombustion products.

It is a general object of the invention to provide a new and improvedfan structure for induced draft boilers.

In the past, induced draft boiler installations utilizing fans forinducing a draft have been of rather complicated and cumbersomeconstruction, wherein the fan and its housing have been a separatestructure apart from the boiler itself. This arrangement required thatseparate duct work be provided from the combustion products tubes to thefan, and additionally required duct work leading from the fan to anexhaust stack for disposing of the combustion products after their usein the boiler. Such arrangements have required an expensive originaloutlay and have been diflicult and costly to maintain.

With the above and other considerations in mind, it is an object of thisinvention to simplify fan structures in induced draft boilers.

Another object is to provide in an induced draft boiler anew andimproved fan structure which is compactly arranged and easily accessiblefor repair and maintenance.

A further object is to provide a new and improved fan structure forinduced draft boilers, wherein the fan is mounted in a chamber formed inthe boiler shell between a tube sheet and a head plate in communicationwith the passes for combustion products so as to draw air fromatmosphere to a burner located in the fire tube and to draw combustionproducts from the burner through multiple passes in the boiler and todeliver same to an exhaust outlet.

Other objects and advantages will become readily apparent from thefollowing detailed description taken in connection with the accompanyingdrawings, in which:

Fig. 1 is a vertical sectional view, partly in elevation, taken throughthe center of a boiler structure embodying the present invention;

Fig. 2 is an end elevational view, partly in section, and with the fanwheel removed, taken at about the line 2-2 of Fig. 1; and,

Fig. 3 is a fragmentary sectional view, taken at about the line 33 ofFig. 1, illustrating the construction of the fan wheel.

-While. an illustrative embodiment of the invention is shown in thedrawings and will be described in detail herein, the invention issusceptible of embodiment in .many different forms, and it should beunderstood that the present disclosure is to be considered as anexemplir 2,888,910 Patented June 2,1959

fication of the principles of the invention and is not intended to limitthe invention to the embodiment illustrated. The scope of the inventionwill be pointed out in the appended claims.

Referring now to the drawings, as illustrated, the invention is embodiedin a boiler having an outer tubular shell 10 covered with insulatingmaterial. Tube sheets 11 and 12 are mounted in the shell 10 in spacedrelation to the ends of the shell and support a fire tube 13 of arelatively large diameter extending lengthwise of the shell. The leftend of the shell, as viewed in Fig. 1, is closed by a head plate 14which may be removably attached to the end of the shell by means such asbolts or screws, not shown. The fire tube 13 extends through the headplate 14 and is open to atmosphere to admit air, as indicated by arrows15, to the fire tube and to a burner 16 situated in the fire tube. Fuel,either gas or oil, may be supplied to the burner 16 through a conduit 17from a source not indicated.

Tube sheets 11 and 12 also support additional, relatively small tubes 13which provide multiple passes through the shell for gases includingproducts of combustion from the fire tube. The right end of the boilershell is closed by a head 19 constructed of refractory material andfashioned with a baffle 20 to direct gases emerging from the fire tube13, which forms the first pass, to the smaller tubes 18 below the levelof the baflie 20, the latter tubes forming the second pass through theshell for gases from the fire tube. At the left end of the shell, asviewed in Fig. 1, a bafiie 21, which may be of suitable metal protectedby refractory, is mounted between the tube sheet 11 and the head plate14 to direct gases from the second pass to tubes 18 above the level ofbaffle 20 and below the level of bafiie 21, these tubes forming thethird pass. Gases emerging from the third pass at the right end of theshell above the baffle 20 return to the left through tubes 18 above thebaflle 21, tiger; tubes forming the fourth and final pass through the se In order to establish a draft for drawing air from atmosphere into thefire tube and to pull the gases including combustion products from thefire tube through the multiple passes, the present inventioncontemplates the use of fan structure forming an integral part oftheboiler construction itself. Accordingly, a fan Wheel 25 and itsdriving motor 26 are mounted on the head plate 14. The motor is mountedexteriorly on the head plate and has its drive shaft 26 projectingthrough the head plate, and the fan wheel is mounted on the shaftinteriorly of the shell with one side of the fan wheel closely adjacentthe head plate 14 and separated therefrom by only a running clearance.

The fan wheel, as illustrated, is of a type having radial blades 27outstanding on a full shroud 28 extending from a central hub 29. As seenbest in Fig. l, the inner termini of the blades are slightly spaced fromthe hub where air is drawn into the wheel, and the height of the bladestapers downwardly toward the outer periphery of the wheel. The type ofwheel may be changed from that illustrated since it could be entirelyopen, semi, or fully shrouded. The blades illustrated extend alongradial lines from the hub; however, they may be curved ineither forwardor reverse direction. A single suction wheel is illustrated in thepresent embodiment; however, a double suction may be provided ifdesired.

The fan wheel is received in a chamber 30 formed in part by adish-shaped, casing-like part 31 which is supported on the bathe 21 andmay be secured to the tube sheet 11 or shell by suitable means such aswelding or sheet metal screws. The formation of the chamber 30 in whichthe fan is received is completed by the head plate 14 which fits againstthe open side of the part 31 when the head plate is mounted on the endof the shell 10 The part 31 includes a cylindrical wall 32 whichencircles the periphery of the fan wheel in spaced relation thereto andforms between the wall and the fan an annular duct 33 (Fig. 3). Thedished portion of the casing-like part 31 provides a generally flat wall34 of a size and shape corresponding to that of the fan wheel 'at itsopen side so that when the fan is received in the chamber 30 the wall 34shrouds one side of the fan with only a running clearance between thefan blades and the Wall; The wall 34 is formed with a circular inletopening 35 centrally disposed relative to the fan wheel so that gasesemerging from the last of the multiple passes to the area between tubessheet 11 and head plate 14 above the baffle 21 are drawn into thechamber 30 by'the operation of the fan. I --The cylindrical wall 32 andthe wall 34 of the casinglike part 31 are blended together at the top toform a passage 36 leading from the chamber 30 to an exhaust fitting 37provided on the upper part of the shell 10 and adapted to be connectedwith a suitable stack providedtfor the purpose of disposing of the gasesafter their use in the boiler. The part 31 may be easily formed in aneconomical manner from sheet metal.

Inoperation, the fan may be controlled either automatically ormanuallytorun in a manner found suitable forthe particular installation and whenrunning is confined inthe chamber on one side by the head plate Hand .onthe opposite side by the wall 34 of the casing part 31so that itfunctions to push gases in the chamber 30 radially outwardly of the fanwheel and along the annular duct 33 to the exhaust fitting 37 to which asuitable stack may be connected. This operation will be eflfective todraw gases from the area between tube sheet 11 and head plate 14 abovethe bafile 21 into the chamw ber,.30 through inlet opening 35. The draftthus created is. efiective to draw air from atmosphere into the firetube tothe burner and to draw gases including the products'of combustionthrough the fire tube and through the multiple passes provided by tubes18.

It can now be appreciated that the fan structure provided is ofsimplified construction, compactly arranged within the boiler shell andyet readily accessible simply by removal of the head plate formaintenance and repair, thus securing reduced initial costs and savingsin operation and maintenance.

I claim:

1. In a horizontal fire tube boiler having an outer tubular boilershell, upright tube sheets mounted in the shell in positions spaced fromeach other and spaced respectively from opposite ends of the shell,upright head plates closing opposite ends of the shell and spacedrespectively from the tube sheets to form gas pass areas between thetube sheets and the head plates, horizontally disposed partitionsrespectively dividing the two gas pass areas each into two gas passchambers thereby forming four gas pass chambers, a fire tube supportedon the tube sheets and having one end opening into a first one of saidgas pass chambers, a fuel burner in the fire tube, means forming apassage for admitting combustion air to the opposite end of the firetube, a plurality of additional tubes supported on the tube sheets andforming multiple gas passes leading from said first gas pass chamber tothe fourth one of said gas pass chambers, and an exhaust fitting on theshell adjacent said fourth chamber, in combination therewith, an induceddraft fan structure,

comprising a fan motor having a base secured on the outside of the headplate adjacent said fourth chamber and a drive shaft projecting throughthe head plate into the fourth chamber, a suction fan wheel secured onthe drive shaft in the fourth chamber with only running clearancebetween one side of the fan wheel and the inside of the adjacent headplate, a partition member dividing said fourth chamber into an exhaustchamber communicating with the last of said multiple gas passes and afan chamber communicating with said exhaust fitting, said partitionmember including an upright wall portion adjacent and spaced from theopposite side of the fan wheel by only running clearance and having anopening therethrough opposite a central portion of the fan conmeetingthe exhaust chamber and the fan chamber, and said partition memberincluding a cylindrically shaped wall portion joined to the upright wallportion and encircling'the periphery of-the fan wheel in concentricspaced relation thereto to define an annular duct surrounding the fanwheel and communicating with said exhaust fitting so that rotation ofthe fan wheel is efec tive to draw air into the fire tube to the burnerand to draw combustion products through the multiple passes and deliversame to the exhaust fitting.

2. In a horizontal fire tube boiler having a tubular boiler shell, anupright tube sheet mounted in the shell adjacent one end thereof, a headplate spaced from said tube sheet and closing said one end of the shell,means including said shell, said tube sheet and said head plate forminga gas chamber in the upper portion of said shell at the end thereof,means forming a combustion charn her in the shell having an air inletmeans at one end and an outlet at the other end, a burner in thecombustion chamber, means including tubes supported on the tube sheetforming gas passes leading from the combustion chamber outlet to saidgas chamber, and an exhaust fitting on the shell connecting said gaschamber to atmosphere, in combination therewith, an induced draft fanstructure, comprising, a fan motor having a housing secured on theoutside of the head plate adjacent said gas chamber and a drive shaftprojecting through the head plate into the gas chamber, a fan wheelsecured on the drive shaft in the gas chamber with only runningclearance between the fan wheel and the head plate, a partition memberdividing the gas chamber into an exhaust chamber communicating with saidgas passes and a fan chamber communicating with said exhaust fitting,said partition member including an upright wall portion having onlyrunning clearance with said fan wheel and having an opening therethroughconnecting the exhaust chamber and the fan chamber and centrallydisposed relative to the fan wheel, and said partition member havingarcuate wall portions extending from the upright wall portion outwardlyto the head plate and skirting the periphery of the fan wheel inconcentric spaced relation thereto to define an annular duct surroundingthe fan wheel and open at the top to the exhaust fitting so that onrotation of the fan wheel air is drawn into the combustion chamber andcombustion gases are drawn from the combustion chamber and delivered tothe exhaust fitting.

3. In a stationary boiler having an outer tubular shell, a tube sheetextending transversely in the shell adjacent one end thereof, meansincluding a head plate spaced outwardly from the tube sheet forming agas chamber at said one end of the shell between the tube sheet and thehead plate, means forming a combustion chamber in the shell having anair inlet means at one end and an outlet at the other end, a burner inthe combustion chamber, means including tubes supported on the tubesheet forming gas passes leading from the combustion chamber outlet tosaid gas chamber, and an exhaust fitting opening from the gas chamber toatmosphere, in combination therewith, an induced draft fan structure,comprising, a partition dividing said gas chamber into an exhaustchamber communicating with said gas passes and a fan chambercommunicating with said exhaust fitting, said partition including a walladjacent but spaced from the head plate and having an opening connectingthe exhaust chamber and the fan chamber, a fan motor having a basesecured on the outside of the head plate and a drive shaft projectinginto the fan chamber, a fan wheel secured on the drive shaft in the fanchamber between the head plate and the wall with the central portion ofthe fan wheel opposite said connecting opening and with only runningclearance between the fan wheel and the head plate and between the fanwheel and said References Cited in the file of this patent UNITED STATESPATENTS 1,076,142 Mellin Oct. 21, 1913 1,388,655 Lower Aug. 23, 19212,554,092 De Poray May 22, 1951 2,677,353 Sharp May 4, 1954

